Nowadays, composite materials are used very frequently in the aerospace application due to their superior mechanical properties. Materials used in commercial aircrafts are subject to the stringent flammability regulations set by Federal Aviation Administration. In this context, the peak heat release rate (PHRR) is one of the most important criteria. In the present work, fire behavior of glass phenolic composite is assessed at micro (Thermo-Gravimetric Analysis [TGA]) and small scale (ISO 5660 cone calorimeter). TGA tests are performed under air and inert atmospheres and cone calorimeter tests are performed at three different heat fluxes (25, 35, and 50 kW m−2) using two different kinds of sample holders: a normal (i.e. ISO-5660 standard) sample holder and an insulated one. The results show that PHRR obtained in case of an insulated sample holder is higher than the study case with the normal sample holder. Another important result confirms that if the surface temperature reaches its threshold limit, the total mass lost percentage for glass fiber phenolic composite in the cone and TGA is similar. In addition to the cone study, permeability analysis is also performed on the same materials which are exposed to different heat fluxes. The results from permeability study confirm that the permeability of the material increases as they are subjected to the thermal attack.